GRANT=6673599;P20RR Decreased hippocampal volume and reduced glial cell number in the cortex have been documented in major depression. Based largely on animal studies, stress-induced hypercortisolemia, leading to neurotoxicity and/or Active Cell Death (apoptosis) is the probable cause of the hippocampal volume loss in depression. Active Cell Death is known to involve NMDA glutamate receptor (NMDA-R) activation and nitric oxide overproduction. Agmatine, an endogenous polyamine derived from decarboxylation of arginine and mainly stored in synaptic vesicles of neurons, has been found to antagonize both NMDA-R and Nitric Oxide synthase, and thereby to possess natural neuroprotective properties (i.e., shown against hypoxic ischemia). Hippocampal volume loss has been well-established to occur in animal models of chronic stress. Agmatine is normally abundant in the hippocampus where it may normally be co-released with glutamate to protect from excito-neurotoxicity through a polyamine site in the NMDA-R of normal rats. We hypothesize that in subjects suffering from major depression, agmatine becomes depleted as a consequence of long term release under prolonged stress, and therefore the hippocampal neurons become exposed to neuronal damage. The goal of my proposal is to examine the neuroprotective properties of agmatine against neurotoxicity induced by excitotoxins or higher concentrations of glucocorticoids as have been detected in patients with major depression. To address this goal, the neuroprotective effects of agmatine will be measured in 1) cultured fetal rat hippocampal neurons exposed to glutamate as well as related chemicals, or high concentrations of glucocorticoids in vitro which mimic conditions found in depressed patients in vivo, 2) the hippocampi of rats treated with excitotoxins, and 3) the hippocampi of rats after undergoing chronic mild stress. Concentrations of endogenous agmatine in hippocampi will be correlated with the extent of structural injury to neurons and glial cells in the hippocampal primary culture and in the hippocampus in vivo of treated rats and the rat chronic mild stress model. This research is designed to elucidate the functional significance of agmatine as an endogenous neuroprotective agent of relevance to the effects of chronic stress as occurs in depression. Clarification of structural and biochemical changes in the hippocampus of the chronic mild stress animal model will add to evidence of hippocampal neuron loss in depression, and hopefully suggest ways to augment agmatine's natural neuroprotective effects.